1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a flip-chip BGA (Ball Grid Array) semiconductor device.
2. Description of the Related Art
In the process of assembling a flip-chip BGA, the substrate is normally cleaned after soldering IC chips to the substrate by means of balls. If this cleaning is inadequate, substances such as flux that is used in soldering will not be completely removed from the substrate, and these substances will remain as a residue on the substrate surface or chip surface. This residue is one factor that can cause a decrease in the assembly yield.
Japanese Patent Laid-Open Publication No. H10-041350 discloses one substrate cleaning method of the prior art. In this method, enclosure walls 121 are provided around a cleaning area that includes the mounting area of semiconductor chip 114 on substrate 111, as shown in FIG. 1 and FIG. 2. Cleaning fluid 131 flows into the space that is enclosed by enclosure walls 121. Aperture 116 is formed in the bottom surface of substrate 111, and cleaning fluid 131 that has flowed in is discharged from aperture 116. At this time, cleaning fluid 131 that flows toward aperture 116 flows through gaps between contact pads 115 that are arranged between semiconductor chip 114 and substrate 111, and this flow of cleaning fluid 131 produces the cleaning effect.
It has now been discovered that this cleaning method has the following problems:    (1) To obtain an increased cleaning effect, a rapid flow of cleaning fluid 131 between semiconductor chip 114 and substrate 111 is advantageous, but cleaning routes 141 are not straight, and a rapid flow of cleaning fluid 131 is therefore difficult to achieve.    (2) A cleaning process cannot be performed for vertically stacked substrates 111, and the production efficiency is therefore impaired.    (3) The necessity of forming aperture 116 in the middle of substrate 111 reduces the area that can be used for routing lines on substrate 111 and thus restricts the freedom of line routing.
In the prior art, an adequate cleaning effect could not be obtained due to the above-described points (1) and (2), and residue therefore tended to remain on substrate 111. Residue that remains may prevent underfill resin, which is subsequently injected between substrate 111 and semiconductor chip 114, from achieving adequate bonding with substrate 111 or semiconductor chip 114, and therefore may cause defects in the close adhesion of the underfill resin.